1. Field of the Invention
The present invention relates to a method of forming a pattern of a mask used in depositing an organic material on a pattern area of an organic electroluminescent display, and more particularly, to a method of forming a shadow mask pattern, in which tension is uniformly applied to a pattern area while a pattern is spirally formed in a mask for organic material layer deposition, thereby preventing the pattern from bending or deflecting out of plane.
2. Discussion of the Background
An electroluminescent display, which is a type of flat panel display, can be classified as either an inorganic electroluminescent display or an organic electroluminescent display, according to the type of material used as an emission layer. Recently, the organic electroluminescent display has been used because it can be driven with a low voltage, be lightweight and thin, have a wide viewing angle and have a fast response time for displaying images.
A conventional organic electroluminescent display has an organic electroluminescent device with an anode, an organic material layer, and a cathode stacked on a substrate. The organic material layer includes an organic emission layer, which emits light when a hole recombines with an electron. To transport the hole and the electron to the emission layer and improve emission efficiency, an electron injection layer and an electron transporting layer can be interposed between the cathode and the organic emission layer, and a hole injection layer and a hole transporting layer can be interposed between the anode and the organic emission layer.
An organic electroluminescent device with this configuration can be fabricated by a physical vapor deposition method, including a vacuum deposition method, an ion plating method, or a sputtering method, or by a chemical vapor deposition method using gas reaction. When the organic electroluminescent device is fabricated using one of these methods, a mask with a pattern can be used to deposit the organic material layers in a desired position on a substrate. The mask can be fixed on a mask frame and under tension.
Referring to FIG. 1, to form an organic material layer (not shown) in a pattern on one side of a substrate 1, a mask 3 with a pattern area 3a, where the pattern area 3a pattern corresponds to the pattern of the organic material layer to be formed, can be fastened to a mask frame 5 by, for example, welding, so that the mask 3 is tensioned in the directions shown by arrows ‘A’. Then, a gaseous organic material can be supplied from an organic material effusion cell (not shown) in the direction shown by arrow ‘B’, and the gaseous organic material can be deposited on the substrate 1 through an opening 5a of the mask frame 5 and through the pattern area 3a of the mask 3, thereby forming the organic material layer with a pattern that corresponds to the pattern of pattern area 3a. A mask attaching portion 3b is positioned along the perimeter of, and separate from, the pattern area 3a, and a mask frame attaching portion 5b is positioned along the perimeter, and separate from, the opening 5a. The mask frame 5 and is fastened to the mask 3 by fastening the mask attaching portion 3b and the mask frame attaching portion.
As shown in FIG. 2, a mask pattern can be formed on a mask 3′ by a pattering forming device (not shown). When the mask 3′ is fastened to the mask frame 5 to form the mask pattern on the mask 3′, the pattern forming device is moved from a first side to a second side of the pattern area 3a′ of the mask sheet 3′, for example in a direction shown by arrow ‘C,’ while a tension force is applied to the mask 3′ in a direction shown by arrow A.
Where the mask pattern is formed on the mask 3′ as described above, the tension applied to the mask 3′ creates a reduction in pattern area 3a′ stiffness between adjacent patterns. Thus, as the mask pattern is formed on the mask 3′ under tension in directions shown by arrows A, the stiffness of the mask pattern previously formed is reduced, thus resulting in non-uniform stiffness across the mask pattern.
The non-uniform stiffness can then result in the mask 3′ being bent or deflected out of plane due to the applied tension. Particularly, distortion of the mask 3′ can occur when the mask pattern is formed for thin film deposition, thus making it difficult to form the desired mask pattern on the mask 3′.